SQL Server Always ON --Adding database on 3rd node downtime required?

Scenario:
SQL/OS versions: SQL Server 2012 SP2/windows server 2012 R2
DataCenter1: 
Server1
  TestDB1
DataCenter2: 
  Server2
   TestDB1
Always ON configured with synch-mode, automatic failover Datacenter1 to DataCenter2
AlwaysON Availability Group created from Datacenter1 to DataCenter2

We have DataCenter3(DR) and want to configure Always ON Asynch mode from DataCenter1 - DataCenter3 for TestDB1 database.
DataCenter3
Server3
 TestDB1

Question: 
Do we need any down time to configure Always ON ASynch-mode for adding TestDB1 database from  DataCenter1 - DataCenter3 ?
(After adding the 3rd node into cluster, will add database from DataCenter1 - DataCenter3)


Thanks