In 2016, it was announced that All My Children alumnus James Patrick Stuart had joined the cast in the mystery role of Theo – who is revealed to be Valentin.

Stuart's performance has been met with critical acclaim, having garnered him three consecutive Daytime Emmy Award nominations for Outstanding Supporting Actor in a Drama Series in 2020, 2021 and 2022.

In October 2009, a deathly ill Helena Cassadine (Constance Towers) confides in her longtime enemy Luke Spencer (Anthony Geary) that she needs his help to fend off her evil stepson Valentin.

Theo announces his plans to leave the island when the storm clears only to return and take several hostages at gun point and reveal himself to be Valentin.

He then separates Nikolas and Ava Jerome (Maura West) from the group, demanding he sign over his entire fortune in exchange for Valentin sparing the lives of his friends and family.

When Valentin threatens to kill Ava anyway, a struggle ensues and Nikolas is seemingly shot falling out a window to his presumed death.

[8] Valentin decides his plan isn't working and while escaping himself sabotages the group's boat, stranding them on the island until a mysterious woman comes to their aid.

Using his alias, Valentin makes his way to Port Charles where he has a one-night stand with Nina Reeves (Michelle Stafford), accidentally leaving behind his phone as he goes off to kidnap his grand nephew Spencer (Nicolas Bechtel).

His plans are foiled when Nina finds the phone and tips off Jason and Spencer's uncle, Sonny Corinthos (Maurice Benard), allowing PCPD commissioner Jordan Ashford (Vinessa Antoine) to make the arrest.

As Valentin is extradited to Greece, he assures Lulu Spencer (Emme Rylan) and Dante Falconeri (Dominic Zamprogna) he isn't involved in her father's apparent death and he also promises to see Nina again despite her turning him in.

Meanwhile, WSB Agent Anna Devane (Finola Hughes) puts Valentin on notice that he will regret causing trouble for anyone in Port Charles.

With the help of her colleague Diane Miller (Carolyn Hennesy), Alexis discovers Mikkos had changed his will before his death, willing the family fortune to his oldest living male heir, Valentin.

In late September 2009, it was announced that Matt Borlenghi, best known to daytime viewers for his portrayal of Brian Bodine on All My Children had been cast in the role of Valentin Cassadine.

[10] Borlenghi expressed his excitement about joining the cast, admitting that he always wanted to work on the series; "I can't imagine anywhere I'd rather be right now" he continued.

"[12] On June 16, 2016, Soap Opera Digest reported that another All My Children alumnus James Patrick Stuart known for his portrayal of Will Cortlandt would debut in July.

[15] At the time, "I was bouncing between soccer games with my children and all of a sudden" Stuart's agent contacted him about Frank Valentini's interest in him for the role.

[16] While he was flattered to have been handpicked for the role, Stuart credits his close friends Ricky Paull Goldin and Michael E. Knight (also former co-star) with convincing him to sign on.

"[21] Borlenghi was expected to make his debut on October 14, 2009, and the actor had already reported for his first day of work when he learned of plans to postpone the role due to several creative changes behind the scenes, including the departure of Sarah Joy Brown as Claudia Zacchara, Jonathan Jackson returning to the role of Lucky Spencer replacing Greg Vaughan and the arrival of James Franco.

"[11] In December 2009, Soap Opera Digest reported that the producers wanted Valentin "beefed up" and made plans to pen a "powerful story" for his arrival.

[23] In February 2010, Constance Towers commented on the character's delayed introduction: "We have been serenading his entrance for quite awhile, [sic] but he hasn't made it yet.

On July 1, 2016, Jamey Giddens of Daytime Confidential reported that James Patrick Stuart's character Theo was to be revealed as the infamous Valentin Cassadine.

[20] While the revelation of his true identity shocks everyone on Cassadine Island, head writer Jean Passanante hinted that it would also "leave at least one of them fighting for their life.

"[26] While Valentin does not intend to harm his nephew Nikolas (Stabile), he isn't fazed by his presumed death which he knows benefits him in the long run.

[18] After wrapping his first stint, Stuart wasn't aware of any plans to bring Valentin back until he was contacted by the series several weeks prior and they told him "We've got a ton of stuff for you to do!

[32] Upon his arrival in Port Charles, Valentin takes a romantic interest in Nina Clay (Michelle Stafford) and they have a one-night stand.

"[40] Donald Thompson of Canyon News believed that Valentin was "evil enough" to fulfill the much-needed role of a resident villain, which the series had not had since Helena Cassadine's demise.