He published in 1523 in Antwerp a mathematical treatise entitle Assertionis fidei adversus astrologos sive de significationibus coniunctionum superiorum planetarum anni 1524, which established his reputation in this field.

While staying at Wittenberg, de Schepper published a couple of pamphlets to defend Christian's claims against Fredrick of Holstein and the City of Lubeck who had joined the king's opponents to remove him from the throne.

He returned to the Low Countries in time to comfort Isabella of Austria, the wife of Christian II and sister of Charles V, on her deathbed on 19 January 1526 at Zwijnarden, near Ghent.

[3] Following Isabella's death, he felt that as a Flemish he should rather try to enter the Emperor's service so during the spring of 1526 he probably travelled back to Spain and became close to the Imperial Chancellor Mercurino di Gattinara.

After Gattinara's death, Valdés and de Schepper attended the Diet of Augsburg where they participated in some conciliatory negotiations with Lutheran representatives such as Philip Melanchthon and Justus Jonas, although they failed to produce any agreement.

In 1533 he joined Ferdinand's ambassador Jeronimo de Zara in a peace mission to Constantinople where they met Suleiman the Magnificent and his Grand Vizier Ibrahim Pascha, as well as the Venetian Alvise Gritti who was held in high esteem by the Turkish emperor at that time.

The Flemish artist Pieter Coecke van Aelst also joined de Schepper's party to Constantinople in the hope of convincing the Turkish sultan to give him commissions for tapestries.

The mood at the Ottoman court had shifted following pressures on the Persian border, and both the Grand Vizier Ibrahim Pascha and his protégé Alvise Gritti were starting to lose their influence with Suleiman.

By 1542 he was back in the Low Countries and conducted numerous missions for Mary of Hungary to support her policies towards the German princes as well as her efforts to build war defences.

Maximilian of Burgundy and de Schepper corresponded with Mary of Hungary during periods of war on an almost daily basis to keep her informed about the activities at sea and to issue recommendations.

In 1524 he published “Assertionis fidei adversus astrologos sive de significationibus coniunctionum superiorum planetarum anni 1524”, an extensive contribution to the widespread debate that was instigated by predictions of catastrophic floods following the Great Conjunction of 1524.