Its a windfall and should be handed over to the IVA.
IVA started March 2011, Completed March 2016 and certificate issued 11 days after final payment. It was not always easy but then some of the best decisions aren't.
Sorry Diana - as everyone has said its an 'additional' asset of your IVA and is caught under the windfall clause so has to be paid over. Non disclosure/payment could result in a failure of the IVA.