Depicted on the boss of the vault at the east end of the south choir aisle are portraits of Edward IV and Richard Beauchamp, bishop of Salisbury, kneeling before a Celtic cross. The cross in question is the Cross of Gneth, a reliquary of the True Cross taken from the body of the last native Prince of Wales Llywelyn ap Gruffudd at his death in 1282. An object of widespread devotion in Wales it then became a valued trophy of Edward I, the conqueror of Wales. He got possession of this relic in 1283 and his particular veneration of it savours of devotion spiced by triumph.

The Cross of Gneth was subsequently given to the college by Edward III shortly after its foundation. It was destroyed at the Reformation and the precise site of its display within the south choir aisle is not now known. Possibly it stood on a lost altar beneath the boss. The 15th-century inscription of Bishop Beauchamp in the adjacent niche makes explicit reference to it and it must, therefore, have been visible from this point.