Alexander Forbes Irvine, 20th Laird of Drum FRSE JP DL LLD (1818–1892) was a Scottish landowner, advocate, philosopher and amateur astronomer.

He was a prominent member of Clan Irvine and held the family seat of Drum Castle until his death.

Other friends included William Forbes Skene of Rubbislaw and Sir David Lindsay.

In 1875/1876, he arranged for a restoration of the courtyard, and the addition of an arched entrance and angle tower.

In 1848 he married Anna Margaretta Forbes-Leslie (d.1900), daughter of Lt Col Jonathan Leslie of Rothienorman, a noted amateur archaeologist.